THat's tough, I'm sorry
What's your ammonia and nitrates?
Goonch stress easily if those numbers aren't flawless (0,0,20 OR LESS) and tend to freak out. If they're being harassed by other fish, they freak out. If theres a sudden change in water conditions, they freak. If pretty much anything happens, they freak.
These freakouts often result in the fish swimming violently and sarcastically around the tank, resulting in the fish smashing into the glass, killing itself. One goonch freaking out can set off the others.
There's been a few documented instances of goonch self destruction like this, and there's no clear cause for the initial freakout.